1. Field Of The Invention
The invention relates to color video and computer displays and to an improved apparatus and method for producing a full color video or computer display using a light modulator such as a liquid crystal panel.
2. Description Of The Prior Art
Transmissive light valve matrix panel displays (such as liquid crystal image panels) use an x:y matrix of scanned horizontal and vertical conductive stripes. The intersection of these stripes define pixels of variable light transmission which are the basic picture elements. Together, these pixels form the image on the panel. Each horizontal or vertical stripe requires an individual electronic driving element, hereinafter called driver, which is usually part of a special purpose integrated circuit. The stripes are electronically scanned in order to control the monochromatic transmission (i.e., brightness) of the pixels, thereby forming an image.
There are several currently known means for producing color from such a light valve matrix display. As an example, first means for obtaining color with such a display is to overlay the monochromatic matrix with an arrangement of primary color filters in the form of stripes or pixel-sized dots so that closely spaced groupings (usually consisting of three primary colors: i.e., red, blue and green) spatially merge when seen by the eye. Such a grouping of pixels is sometimes referred to in the literature as a "pel." In this case, each pel is composed of three pixels and requires three drivers. A color display made by this means sacrifices resolution for the sake of color, there being three times as many pixels (i.e., red, blue and green) as in a monochromatic display of equivalent resolution.
A second means for producing color images is to use three separate monochromatic panels, one for each primary color. The images from each of these panels is filtered and optically merged to create a single color image for the viewer. As in the first example, three separate pixels (and associated driving electronics) are required in the formation of a single pel.
There are still other means for obtaining color images involving partial polarization, interference phenomena and special diffraction phenomena.
Additionally, an example of a prior attempt to provide a means for producing a natural color display is seen in U.S. Pat. No. 4,978,952 to Irwin. Which discloses a display including a matrix of horizontal and vertical elements illuminated by light emitting diodes (LEDs) and gated by a liquid crystal light valve.
The Irwin device requires three separate drivers and light sources for each pel. Thus, in a viewing screen comprising 640 color pels across, the Irwin device would require 1,920 separate vertical drivers. Since the Irwin device has difficulty achieving minimal weight and flexible weight distribution, it would not be useful for head mounted display systems where weight must be minimized and weight distribution must be considered.
Furthermore, Irwin creates the picture by selective blocking of light with horizontal liquid crystal shutter elements. The use of shutter elements, in combination with the other elements used to drive the display, results in a display with relatively high power consumption and low efficiency. For example, if the display disclosed in the Irwin patent were comprised of 640 vertical elements, then less than 1/640th of the light input generated by the LEDs would be used at any given time for pixel illumination.
Earlier video systems, such as the frame sequential CBS/RCA television systems, used cathode ray tubes and spinning color wheels. By their nature they were limited in both size and definition by the requirement that the color wheel be substantially larger than the screen face and that it be of high optical quality.